ssd1306: add options to customize the hardware pin layout (#282)

Fixes #166

devices/ssd1306/ssd1306.go

@@ -57,6 +57,8 @@ var DefaultOpts = Opts{
 	W:             128,
 	H:             64,
 	Rotated:       false,
+	Sequential:    false,
+	SwapTopBottom: false,
 }
 
 // Opts defines the options for the device.
@@ -65,6 +67,14 @@ type Opts struct {
 	H int
 	// Rotated determines if the display is rotated by 180°.
 	Rotated bool
+	// Sequential corresponds to the Sequential/Alternative COM pin configuration
+	// in the OLED panel hardware. Try toggling this if half the rows appear to be
+	// missing on your display.
+	Sequential bool
+	// SwapTopBottom corresponds to the Left/Right remap COM pin configuration in
+	// the OLED panel hardware. Try toggling this if the top and bottom halves of
+	// your display are swapped.
+	SwapTopBottom bool
 }
 
 // NewSPI returns a Dev object that communicates over SPI to a SSD1306 display
@@ -287,22 +297,30 @@ func newDev(c conn.Conn, opts *Opts, usingSPI bool, dc gpio.PinOut) (*Dev, error
 		// Signal that the screen must be redrawn on first draw().
 		scrolled: true,
 	}
-	if err := d.sendCommand(getInitCmd(opts.W, opts.H, opts.Rotated)); err != nil {
+	if err := d.sendCommand(getInitCmd(opts)); err != nil {
 		return nil, err
 	}
 	return d, nil
 }
 
-func getInitCmd(w, h int, rotated bool) []byte {
+func getInitCmd(opts *Opts) []byte {
 	// Set COM output scan direction; C0 means normal; C8 means reversed
 	comScan := byte(0xC8)
 	// See page 40.
 	columnAddr := byte(0xA1)
-	if rotated {
+	if opts.Rotated {
 		// Change order both horizontally and vertically.
 		comScan = 0xC0
 		columnAddr = byte(0xA0)
 	}
+	// See page 40.
+	hwLayout := byte(0x02)
+	if !opts.Sequential {
+		hwLayout |= 0x10
+	}
+	if opts.SwapTopBottom {
+		hwLayout |= 0x20
+	}
 	// Set the max frequency. The problem with I²C is that it creates visible
 	// tear down. On SPI at high speed this is not visible. Page 23 pictures how
 	// to avoid tear down. For now default to max frequency.
@@ -317,7 +335,7 @@ func getInitCmd(w, h int, rotated bool) []byte {
 		0x40,           // Start display start line; 0
 		columnAddr,     // Set segment remap; RESET is column 127.
 		comScan,        //
-		0xDA, 0x12, // Set COM pins hardware configuration; see page 40
+		0xDA, hwLayout, // Set COM pins hardware configuration; see page 40
 		0x81, 0xFF, // Set max contrast
 		0xA4,       // Set display to use GDDRAM content
 		0xA6,       // Set normal display (0xA7 for inverted 0=lit, 1=dark)
@@ -326,10 +344,10 @@ func getInitCmd(w, h int, rotated bool) []byte {
 		0xD9, 0xF1, // Set pre-charge period; from adafruit driver
 		0xDB, 0x40, // Set Vcomh deselect level; page 32
 		0x2E,                   // Deactivate scroll
-		0xA8, byte(h - 1), // Set multiplex ratio (number of lines to display)
+		0xA8, byte(opts.H - 1), // Set multiplex ratio (number of lines to display)
 		0x20, 0x00, // Set memory addressing mode to horizontal
-		0x21, 0, uint8(w - 1), // Set column address (Width)
+		0x21, 0, uint8(opts.W - 1), // Set column address (Width)
-		0x22, 0, uint8(h/8 - 1), // Set page address (Pages)
+		0x22, 0, uint8(opts.H/8 - 1), // Set page address (Pages)
 		0xAF, // Display on
 	}
 }

devices/ssd1306/ssd1306_test.go

@@ -5,6 +5,7 @@
 package ssd1306
 
 import (
+	"bytes"
 	"errors"
 	"image"
 	"image/color"
@@ -384,7 +385,7 @@ func TestSPI_3wire(t *testing.T) {
 func TestSPI_4wire_String(t *testing.T) {
 	port := spitest.Playback{
 		Playback: conntest.Playback{
-			Ops: []conntest.IO{{W: getInitCmd(128, 64, false)}},
+			Ops: []conntest.IO{{W: getInitCmd(&Opts{W: 128, H: 64, Rotated: false})}},
 		},
 	}
 	dev, err := NewSPI(&port, &gpiotest.Pin{N: "pin1", Num: 42}, &DefaultOpts)
@@ -409,7 +410,7 @@ func TestSPI_4wire_Write_differential(t *testing.T) {
 	port := spitest.Playback{
 		Playback: conntest.Playback{
 			Ops: []conntest.IO{
-				{W: getInitCmd(128, 64, false)},
+				{W: getInitCmd(&Opts{W: 128, H: 64, Rotated: false})},
 				{W: buf1},
 				// Reset to write only to the first page.
 				{W: []byte{0x21, 0x0, 0x7f, 0x22, 0x1, 0x1}},
@@ -441,7 +442,7 @@ func TestSPI_4wire_Write_differential_fail(t *testing.T) {
 	port := spitest.Playback{
 		Playback: conntest.Playback{
 			Ops: []conntest.IO{
-				{W: getInitCmd(128, 64, false)},
+				{W: getInitCmd(&Opts{W: 128, H: 64, Rotated: false})},
 				{W: buf1},
 			},
 			DontPanic: true,
@@ -468,7 +469,7 @@ func TestSPI_4wire_Write_differential_fail(t *testing.T) {
 func TestSPI_4wire_gpio_fail(t *testing.T) {
 	port := spitest.Playback{
 		Playback: conntest.Playback{
-			Ops: []conntest.IO{{W: getInitCmd(128, 64, false)}},
+			Ops: []conntest.IO{{W: getInitCmd(&Opts{W: 128, H: 64, Rotated: false})}},
 		},
 	}
 	pin := &failPin{fail: false}
@@ -489,10 +490,29 @@ func TestSPI_4wire_gpio_fail(t *testing.T) {
 	}
 }
 
+func TestInitCmd(t *testing.T) {
+	tests := []struct {
+		opts         *Opts
+		wantSubslice []byte
+	}{
+		{opts: &Opts{W: 128, H: 64}, wantSubslice: []byte{0xDA, 0x12}},
+		{opts: &Opts{W: 128, H: 64, Sequential: true}, wantSubslice: []byte{0xDA, 0x02}},
+		{opts: &Opts{W: 128, H: 64, SwapTopBottom: true}, wantSubslice: []byte{0xDA, 0x32}},
+		{opts: &Opts{W: 128, H: 64, Sequential: true, SwapTopBottom: true}, wantSubslice: []byte{0xDA, 0x22}},
+	}
+
+	for _, test := range tests {
+		got := getInitCmd(test.opts)
+		if !bytes.Contains(got, test.wantSubslice) {
+			t.Errorf("getInitCmd(%v) -> %v, want %v", test.opts, got, test.wantSubslice)
+		}
+	}
+}
+
 //
 
 func initCmdI2C() []byte {
-	return append([]byte{0}, getInitCmd(128, 64, false)...)
+	return append([]byte{0}, getInitCmd(&Opts{W: 128, H: 64, Rotated: false})...)
 }
 
 var preludeI2C = []byte{